The BNs usually have big "Audition Copy" stamps on the back of the jacket - at least during the Liberty era of the late '60s, that's what they had.
As for Prestige/New Jazz, my few promos have "Review Copy" stamped on one label and on the back of the jacket in small-ish type.
They weren't differentiated by label color like Verve and ABC/Impulse, for example.